hapijs/joi

Analysis updated 2026-06-21

★ 21,194JavaScriptAudience · developerComplexity · 2/5Setup · easy

Mindmap

mindmap
  root((joi))
    What it does
      Data validation
      Schema definition
      Error reporting
    Tech Stack
      JavaScript
      Node.js npm
    Use Cases
      API body validation
      Form data checking
      Type coercion
    Audience
      Backend developers
      Full-stack devs

mindmap root((joi)) What it does Data validation Schema definition Error reporting Tech Stack JavaScript Node.js npm Use Cases API body validation Form data checking Type coercion Audience Backend developers Full-stack devs

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What do people build with it?

USE CASE 1

Validate API request bodies in an Express or hapi.js server to ensure required fields are present and correctly formatted.

USE CASE 2

Define a schema for user registration data and return clear error messages when email, password, or username fail the rules.

USE CASE 3

Sanitize and coerce incoming JSON from external APIs to ensure data types match your expectations before processing.

What is it built with?

JavaScriptNode.js

How does it compare?

	hapijs/joi	gildas-lormeau/singlefile	parse-community/parse-server
Stars	21,194	21,045	21,379
Language	JavaScript	JavaScript	JavaScript
Setup difficulty	easy	easy	hard
Complexity	2/5	2/5	4/5
Audience	developer	general	developer

Figures from each repo's GitHub metadata at analysis time.

How do you get it running?

Difficulty · easy Time to first run · 5min

In plain English

joi is a data validation library for JavaScript. It lets you define schemas, structured descriptions of what your data should look like, and then validate objects, strings, numbers, and other values against those schemas. Based on the description and topics, it is designed to be the most powerful schema description and data validation tool in the JavaScript ecosystem, and is associated with the hapi web framework ecosystem. It is installed via npm and full documentation is available at joi.dev. The README does not provide further detail beyond pointing to the documentation portal.

Copy-paste prompts

Prompt 1

Using joi, write a validation schema for a user registration payload that requires an email, a password of at least 8 characters, and an optional display name, and show me how to validate an object against it and extract error messages.

Prompt 2

I have a joi schema for my API request body. Show me how to use it as Express middleware so invalid requests are rejected with a 400 error and a JSON error message before hitting my route handler.

Prompt 3

Using joi, how do I define a schema where a field is required only when another field has a specific value (conditional validation)?

Prompt 4

Write a joi schema that validates an array of items where each item has a type field that determines which other fields are required, a discriminated union pattern.

Frequently asked questions

What is joi?

A JavaScript data validation library that lets you define schemas describing what your objects, strings, and numbers should look like, then validate real data against those rules and surface clear error messages.

What language is joi written in?

Mainly JavaScript. The stack also includes JavaScript, Node.js.

How hard is joi to set up?

Setup difficulty is rated easy, with roughly 5min to a first successful run.

Who is joi for?

Mainly developer.

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